The present invention relates to a sorting method and a sorting device for sorting particles according to their settling velocities in a fluid medium using gravitational forces for both separation of the particles into groups of particles having similar settling velocities and collection of such separated (grouped) particles in sorted fashion.
The present invention may be useful in detecting the presence of gold in sands. Further, it may provide a basis for a large-scale gold production. The present invention may also be useful in easily sorting several kinds of particles such as granulated anaerobic sludges according to the settling velocities of the granules and thus providing data for evaluating the performance of anaerobic digestion systems.
There are methods currently in use for sorting particles according to their sizes using sieves and according to their settling properties; sorting of particles according to their settling properties include pumping water at increasing upflow velocities into a column where the particles are placed for sorting, and, through an overflow port in the column, the upflow water currents carry the particles "sorted in fractions" corresponding to the upflow velocities themselves.
However, using sieves is associated with operational and maintenance problems resulting from mesh clogging of the sieves. On the other hand, using increasing upflow velocities is time consuming. Moreover, when the particles are delicate in structure, such as granulated anaerobic sludges, methods based on using sieves or upflow velocities tend to subject the particles to shear stress over relatively long periods of time resulting in damage and possible disintegration of such delicate particles. This brings into question the performance and reliability of these methods. This is due to the fact that when larger particles disintegrate into small fragments, the settling properties of the resulting fragments are different from the original particles. Therefore, the fragments do not represent the real status of the original particles before sorting.